Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), flash memory, and resistance variable memory, such as phase change random access memory (PCRAM), resistive random access memory (RRAM), and conductive bridge random access memory (CBRAM), among others.
The phase change material of a PCRAM device may exist in an amorphous, higher resistance state, or a crystalline, lower resistance state. The resistance state of the PCRAM cell may be altered by applying sources of energy to the cell, such as current pulses or pulses of light, among other sources of energy. For example, the resistance state of the PCRAM cell may be altered by heating the cell with a programming current. This results in the PCRAM cell being programmed to a particular resistance state, which may correspond to a data state. PCRAM devices may also be configured to provide multi-level storage. That is, the memory device may have a plurality of discrete and identifiable states which allow for multi-bit storage in a single memory cell.
An RRAM device includes a variable resistive material, such as a transition metal oxide, that has varying resistance depending on voltages applied thereto. When a voltage equal to or greater than a set voltage is applied to the variable resistive material, the resistance of the variable resistive material decreases (e.g., ON state). When a voltage equal to or greater than a reset voltage is applied to the variable resistive material, the resistance of the variable resistive material increases (e.g., OFF state). High volume manufacturability and reliability remain issues for resistance variable memory devices such as PCRAM and RRAM devices.